1. Field of the Invention
This invention relates to edge trimming of metal strip, and more particularly to an improved apparatus for trimming the side edges of a running length of metal strip.
2. Description of the Prior Art
In the production of metal strip, it is conventional practice to roll the strip from a slab or ingot to a width slightly greater than desired for the finished product. After rolling, the strip is edge trimmed along each side to produce the desired strip width and remove any edge defects and irregularities, and to produce uniformly smooth parallel side edges. While the metal ribbon trimmed from each side edge is chopped into short lengths and recycled as scrap, it nevertheless represents a very substantial expense.
Although edge trimming is necessary, for economic reasons, it is desired to trim as little material as practical from the strip. While modern rolling mill practice makes it possible to roll strip to a width near that desired for the finished product, it has generally been considered necessary to trim a ribbon from the side edges which is wider than required to produce the desired parallel edges and to remove edge irregularities and defects. The reason for this is that, in most high speed side trimming operations, it generally has not been considered possible to adequately stabilize the edges of the running length of strip to simultaneously trim very narrow ribbons from both sides of the strip.
The edge trimming of metal strip is conventionally performed by pairs of cooperating disc or wheel-type shearing cutters which may also be equipped with chopping devices for chopping the trimmed ribbon into short lengths of scrap as disclosed, for example, in U.S. Pat. No. 3,110,208. As mentioned in this prior art patent, the rotary shearing cutters tend to cause a transverse bow in the metal strip between the oppositely disposed pairs of cutting shears and it has been proposed to use top and bottom stabilizing guides in contact with the strip. This bowing tendency is not always uniform and can cause distortion in the edge of the strip, producing a ripple-like surface at the edge and an uneven width for the trimmed strip.
It has been proposed to use a stabilizing donut mounted adjacent to and rotating with the rotary shear cutters in a metal strip slitting operation as shown, for example, in U.S. Pat. No. 4,492,135. In the stabilizing device of this patent, a metal tire is urged into contact with the strip surface by a resilient ring supported for rotation with the rotary cutters.
The use of rotary shearing cutters in a high speed edge trimming operation for trimming sheet steel produces rapid wear and dulling of the rotary cutters, with the result that the cutters require frequent adjustment and periodic replacement. Such adjustment or replacement can only be accomplished when the edge trimmer is out of operation and since the edge trimmer is normally operated in conjunction with other strip processing steps such as a pickling and coating line, it is important that such adjustment and/or replacement of the cutters be accomplished in a minimum of time. The prior art trimming devices employing rigid holddown guides presented serious obstacles to cutter changing and also required substantial time for adjustment when adjusting the apparatus for processing strip of different widths.
Accordingly, it is an object of the present invention to provide an improved edge trimming apparatus for accurately severing an edge trim ribbon of minimum width from the edges of metal strip.
Another object is to provide such an edge trimming apparatus including rotary strip stabilizing means which provides improved strip stability and eliminates or minimizes transverse strip bowing and edge buckling and distortion during the trimming operation.
Another object is to provide such a strip edge trimming apparatus which is mounted for movement with the rotary cutters for adjusting the apparatus to trim strips of different widths.
Another object is to provide such an edge trimming apparatus which facilitates cutter adjustment and/or cutter changing to thereby minimize down time for the apparatus.